Beginning July 1, 2006, and every year thereafter, the department shall determine the following information for each retired member or beneficiary whose retirement allowance has been in effect for at least one year:
(1) The original dollar amount of the retirement allowance;
(2) The index for the calendar year prior to the effective date of the retirement allowance, to be known as "index A";
(3) The index for the calendar year prior to the date of determination, to be known as "index B"; and
(4) The ratio obtained when index B is divided by index A.
The value of the ratio obtained shall be the annual adjustment to the original retirement allowance and shall be applied beginning with the July payment. In no event, however, shall the annual adjustment:
(a) Produce a retirement allowance which is lower than the original retirement allowance;
(b) Exceed three percent in the initial annual adjustment; or
(c) Differ from the previous year's annual adjustment by more than three percent.
For the purposes of this section, "index" means, for any calendar year, that year's average consumer price index, Seattle, Washington area, for urban wage earners and clerical workers, all items, compiled by the bureau of labor statistics, United States department of labor.